The space shuttle Columbia, which disintegrated during re-entry at the end of a 16 day mission on Saturday was the oldest orbiter in the space agency's small fleet of craft capable of carrying astronauts into orbit. Space agency officials had expected the ship to perform many more missions.

The space shuttle Columbia shared the name of the command module for Apollo 11, the first manned mission to the moon.

Columbia was delivered to NASA from its manufacturer, Rockwell International, in 1979. It took two years to get the shuttle ready for its first flight in April of 1981 - a test orbit around the earth.

Since then, Columbia flew 28 missions, according to NASA spokesman George Diller. "It had some notable missions but probably the most notable is it deployed the first satellite from the space shuttle in 1982, but since then it's had a whole history of missions that included flying the Chandra X-ray telescope and a number of space lab missions and some Department of Defense missions. It really covered the range," said George Diller.

The Columbia astronauts were returning to earth after an otherwise routine 16-day mission that involved a series of science experiments.

This is the second disaster involving a space shuttle. It was January 28, 1986 when the shuttle Challenger exploded shortly after take off, killing seven astronauts, including school teacher Christa McAuliffe.

Despite the dramatic nature of space disasters, there have been remarkably few since President John F. Kennedy committed the United States to putting a man on the moon in the 1960s.

The only other U.S. space agency disaster occurred in 1967, when astronauts Gus Grissom, Edward White and Roger Chaffee died in a fire that swept through their Apollo command module during a ground test at Kennedy Space Center in Florida.

In spite of the age of the shuttle Columbia, NASA spokesman Diller says the ship was continually maintained, and the space agency had planned to keep it in service for many more years. "Columbia, even though it was our first orbiter and our oldest one, had been upgraded to state-of-the art technology on the flight deck," he said. "And in fact we had expected Columbia to continue in the fleet for a long time. Each of the orbiters is designed for 100 flights, and Columbia was on its 28. So, we had upgraded it to keep all of the avionics on the flight deck current and had made a number of structural improvements to it so it could fly heavier payloads and also fly up the international space station."

The Columbia disaster now leaves NASA with three orbiters - the Discovery, Atlantis and Endeavour.